Currently, with unceasing development of mobile communication technologies, the demand for positioning services is also increased day by day. Application scenarios of the positioning services show a diversified trend, e.g., emergency position, crime location tracking, navigation, traffic control, etc. But, no matter how diversified the application scenarios are, the industry always hopes to acquire a reliable, efficient and quick method for satisfying the positioning demand, in other words, positioning technologies which are easy to be implemented and of high precision are always the hot pursuit sought by peoples.
Development of the global positioning system (GPS) enables a mobile station having a GPS module to obtain an accurate positioning, however, disadvantages of the GPS are also relatively obvious; firstly, an addition of the GPS module will necessarily increase the cost of the mobile station, secondly, as a satellite positioning technique, the GPS is not suitable for scenarios of a high-density urban area (shaded by buildings). Although the network positioning does not have a high accuracy as the GPS positioning, it is more suitable for the scenarios of the high-density urban area. Hence, an algorithm combining the GPS positioning and the network positioning is a focus of the current research.
Currently, there are two network positioning schemes: one is an uplink time difference of arrival (UTDOA) positioning method, the other is an observed time difference of arrival (OTDOA) positioning method.
According to the UTDOA positioning method, a user equipment (UE) sends an uplink positioning signal (e.g., a sounding reference signal (SRS), etc.), and an estimation of the arrival time of the uplink signal is performed at an evolved node (eNB) side to obtain distance of the eNB and the UE. Thereby, distance between a plurality of eNBs and the UE is obtained; a relative coordinate position of the UE relative to the eNBs is obtained by calculating according to a triangulation algorithm and the like, and then the network can obtain an absolute position of the UE according to actual positions of the eNBs. However, since the UTDOA positioning method adopts an estimation of the uplink positioning signal of the UE, it is restricted by the uplink transmit power of the UE; since the uplink transmit power of the UE is limited, the cover range of the positioning signal emitted by the UE is also limited, therefore, the number of the eNBs which performs the UTDOA positioning for the UE is restricted and, thus, the positioning precision of the UTDOA is restricted. Meanwhile, the UTDOA is also a positioning algorithm based on an estimation of the signal arrival time, hence, if the positioning signal is sheltered or reflected, the signal arrival time will be affected, thereby affecting the positioning precision.
The principle of the OTDOA positioning method is that, when there are three or more base stations existing in a system, position of a UE can be determined according to time difference of arrival of downlink transmission signals from different base stations. The downlink transmission signals may be positioning reference signals, and may also be synchronization signals. As known from the definition of a hyperbola, the hyperbola is constituted by points satisfying the condition as following: distance difference from the points to two specified points is a constant value. As shown in FIG. 1, in the system, there are a base station 0, a base station 1 and a base station 2, assuming that the black filled portion in FIG. 1 indicates the position of the UE, points which satisfy that distance difference from the UE to the base station 0 and the base station 1 is d1-d0 form one hyperbola, and points which satisfy that distance difference from the UE to the base station 1 and the base station 2 is d2−d1 form the other hyperbola, then, the crossover point of the two hyperbolas is namely the position of the UE. The more the number of base stations existing in the system, the more accurately the determined position of the UE. In the LTE, the OTDOA positioning is used as a technique where the network assists the positioning of the UE, at the network side, after an enhanced serving mobile location centre (e-SMLC) assigns transmit configuration and receive configuration of a positioning reference signal (PRS) for a base station and a mobile station, the base station sends the PRS to the mobile station, after receiving the PRSs from a plurality of base stations, the mobile station recognizes the first arrival path position of each of the PRSs and, thus, can obtain time difference of arrival of the PRSs among different base stations, and then report the time difference to the e-SMLC. The e-SMLC can obtain the distance difference from the mobile station to different base stations according to the received time difference of arrival of the PRSs. By means of the mathematical computation of the foregoing hyperbolic model, the e-SMLC can obtain an accurate position of the mobile station. It is thus clear that the precision of the OTDOA positioning is dependent on the receiving of the PRS signals and the estimation of the first arrival path position to a great extent, therefore, in scenes of a dense urban area, the path of the PRS is not a straight path due to multiple reflections, refractions and attenuations of a signal caused by obstructions from buildings, if an estimation of the position of the mobile station is still performed according to the time difference of arrival of the PRSs, a great positioning error will be brought.